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Jan. 3 1956 G. H. WEBSTER 2,733,288 ELECTRIC CABLES OF THE COAXIALCONDUCTOR TYPE SUITABLE FOR USE FOR CURRENTS AT HIGH FREQUENCIES FiledJan. 30, 1951 2 Sheets-Sheet l SOLDEE 0/? CEMENT /O /O 12? IO 9 InvenlorJOZOEE 0e (6/1454 7 L y U04 fl 1 Attorney Jan. 31, 1956 G. H. WEBSTER2,733,283 ELECTRIC CABLES OF THE COAXIAL CONDUCTOR TYPE SUITABLE OR USEFOR CURRENTS AT HIGH FREQUENCIES Filed Jan. 50, 1951 2 Sheets-Sheet 2 /O1 m 9 $0105? 0 CEMENT 7 mm/mr/on/ 10 8 X 10 9 I0 604 05/? 0A CEME/W"Inventor 0 1+. web-iv.

y 01M mh United States Patent ELECTRIC CABLES OF THE COAXIAL CONDUC- TORTYPE SUITABLE FOR USE FOR CURRENT S AT HIGH FREQUENCIES George HarryWebster, Liverpool, England, assignor to British Insulated CallendersCables Limited, London, Engiand, a British company Application January30, 1951, Serial No. 208,512 Claims priority, application Great BritainFebruary 8, 1950 21 Claims. (Cl. 174-28) This invention relates toelectric cables of the type having conductors formed and arranged so asto be suitable for use for carrying currents at high frequencies. Theinvention refers particularly to the construction of a tubular conductorfor use as part of such a cable, this construction being especiallysuitable for tubes of large diameters, for instance from half an inchupwards. This tubular conductor is of the kind comprising two superposedco-axial layers, each formed by bending transversely a strip of metal toform an approximately complete cylinder, the meeting places of the edgesof the strips being preferably displaced from each other through anangle of from 90 to 180.

In accordance with the invention in such a construction the inner layeris formed with outwardly projecting transverse ribs and the outer layerwith inwardly projecting transverse ribs. The ribs of the two layers areapproximately equal in depth radially and fit between each other and thelayers and ribs are so dimensioned that the layers are spaced apart bythe depth of the ribs. This construction gives, with comparatively thinmetal in each layer, sufiieient circumferential stiffness of each layercombined with longitudinal flexibility of the whole structure andsufficiently close association of the two layers for the electrical andmechanical requirements of the case.

The inner and outer layers in such a construction may be joined togetherby soldering or cementing at points of contact, that is along the ridgesof the ribs. The joining may be etfected at the ribs of one layer only,i. e. the ribs of the inner layer to the inner surface of the outerlayer or the ribs of the outer layer to the outer surface of the innerlayer, or may be effected at both these places. This joining gives animproved mechanical strength while maintaining sufiicient longitudinalflexibility of the whole structure. Alternatively, or in addition, thetwo layers may be bound together by tapes of suitable material.According to the method adopted for securing together the componentlayers of the tubular conductor and the intended application of thecompleted cable, it may or may not be necessary to guard againstundesirable resonance effects in the tubular conductor by conventionalmethods.

The invention will be more fully described with the aid of theaccompanying drawings wherein Figure 1 is a side view, partly inelevation and partly in section, of a fragmental length of a coaxialconductor type of high frequency cable having an outer conductorconstructed in accordance with the invention, parts having been brokenaway to show the construction more clearly.

Figures 3, 5, 7 and 9 are views corresponding to Figure 1 and showingfurther examples of outer tube construction in accordance with theinvention, and

Figures 2, 4, 6, 8 and 10 respectively, are sections on the lines IIlI,IV--IV, VIVI, VIIIVIII, and XX of Figures 1, 3, 5, 7 and 9,respectively, but drawn to a larger scale.

In these drawings the inner conductor is shown as a single wire ofcircular cross-section but it may be of other appropriate form. Theouter conductor 2 is formed by two superposed co-axial layers 3 and 4,each consisting of a strip of metal bent to form an approximatelycomplete cylinder. In the illustrated examples the edges 5, 6 of onemetal strip, lie diametrically opposite those 7, 8 of the other metalstrip but an angular displacement of other than 180 may be adopted, forinstance, or any angle between 90 and The inner conductor 1 is locatedcentrally within the outer tubular conductor 2 by spacing discs 9 ofinsulating material positioned at frequent intervals along the length ofthe conductor.

In each example of construction illustrated, the inner component layerof the outer conductor has outwardly projecting transverse ribs 10 andthe outer component layer has inwardly projecting transverse ribs 11.The ribs 10 and 11 are approximately of the same radial depth and fitbetween each other whereby to space apart the two component layers 3 and4 by the radial depth of the ribs.

Preferably the longitudinal spacing of the ribs is the same for bothlayers, or at least the spacing of the ribs of one layer is asufficiently close approximation to that of the ribs of the other layerto avoid the ribs of one layer gradually riding on those of the otherlayer as manufacture of a cable length proceeds. Satisfactory resultsmay be obtained with a spacing for the ribs of both layers of from onceto twice the mean diameter of the tubular conductors. Alternatively thespacing of the ribs on one layer may be a multiple of that of the ribson the other layer.

In forming the component layers of the tubular conductor, thetransversely bent strips 3 and 4 may be arranged with their longitudinaledges 5 and 6, and 7 and 8, parallel with the axis of the conductor, asshown in Figures l, 3 and 5, or they may be nclined slightly so thatthey run in a helix of long pitch, as shown in Figures 7 and 9.

The ribs 10 (or 11) of each component layer may be so formed and placedthat the two ends of each rib meet or come into line with each otherwhere the edges 5 and 6 (or 7 and 9) approach one another, as shown inFigures 1 and 9, or they may be so formed and placed that, as shown inFigures 3, 5 and 7, this wincidence does not take place. The ribs mayrun normal to the axis of the conductor, as shown in Figures 1 and 9, orthey may be skewed as shown in Figures 3, 5 and 7. The latterarrangement has advantages in that it permits by appropriate skewing ofthe ribs of one or both layers and appropriate spacing of the ribs ofone layer relative to those of the other of obtaining longitudinalinterlocking of the two layers 3 and 4. For example, this locking effectmay be attained if each rib on one layer forms a part of a helical screwthread and each rib on the other layer forms part of a screw thread ofthe same pitch and has a width corresponding to the width of the spacewhich would be formed between successive convolutio-ns of the rib on thefirst layer if that rib had a length in excess of one complete turn, sothat over a part of its length the rib on the said other layer mayengage one side of the rib on the first layer and over another part ofits length it may engage the other side of the same rib, as shown inFigure 5.

it is preferred to make this two-layer construction of tube with theedges 5 and 6 of the inner layer abutting against each other, as shownfor example in Figures 1 and 2, and with a small gap between the edges'7 and 8 of the outer layer so that by tightening down this outer layer,the contact between the edges of the inner layer may be ensured and theinternal diameter of the conductor accurately determined by the width ofthe strip used to form the inner layer. When this has been done a bindermay be applied to hold the two layers in position, for instance, abinder consisting of two tapes 12 greases applied as shown in Figure 1.These tapes 12 may be i of fabric, plastic or copper or, where anelectromagnetic screen is required for the conductor, they may be ofsteel. Alternatively, or in addition, the inner and outer layers may besoldered together at their points of contact, namely, along the ridgesof the ribs of one or both layers, for which purpose the ribs may havebeen pretinned, or the inner and outer layers may be cemented togetheralong the ridges as with a synthetic rubber adhesive. Where the ribshave been pre-tinned soldering may be effected by passing the tubethrough a hot die. The soldering may be facilitated by the applicationof a flux to the surfaces to be soldered before the outer strip isclosed on the inner strip. Where adhesive is used to cement the innerand outer layers together along the ridges of the ribs, the adhesive maybe applied to the ribs during assembly of the two layers, as by brushingor squirting. Adhesion may be secured by passing the tube through aheated die or between hot rolls. Although only Figures 1 and 2 of thedrawings show the longitudinal edges of the inner layer 3 in contact, itwill be appreciated that the longitudinal edges of the inner layers 3 ofthe other examples of construction illustrated may, and preferably will,be brought into abutment and held so either by a binder on the outerlayer or by soldering or cementing the outer to the inner layer at theirpoints of contact, or by both means.

What I claim as my invention is:

1. An electric cable for the transmission of high frequency currents,comprising a tubular conductor comprising two superposed and mutuallyradially spaced coaxial layers each comprising a strip of metal benttransversely to form an approximately complete cylinder havingtransverse ribs projecting towards and extending to the adjacent surfaceof the other of said layers, a plurality of insulating members locatedwithin said tubular conductor at intervals along the length of saidtubular conductor and at least one conductor located within said tubularconductor and insulated therefrom by said insulating members.

2. A tubular conductor for a high frequency cable, comprising twosuperposed and mutually radially spaced co-axial layers each comprisinga transversely bent strip of metal forming an approximately completecylinder, the inner of said layers having outwardly projectingtransverse ribs and the outer of said layers having inwardly projectingtransverse ribs, the ribs of both inner and outer of said layers beingapproximately equal in depth radially and fitting between each other,said layers and said ribs being so dimensioned that said layers arespaced apart by the depth of said ribs.

3. A tubular conductor for a high frequency cable, comprising twosuperposed and mutually radially spaced co-axial layers, each of saidlayers comprising a strip of metal bent transversely to form anapproximately complete cylinder having transverse ribs projectingtowards and extending to the adjacent surface of the other of saidlayers and located between the ribs of the said other layer, thelongitudinal spacing of said ribs being at least approximately the samefor both layers.

4. A tubular conductor as claimed in claim 3, wherein the longitudinalspacing of said ribs is from once to twice the mean diameter of thetubular conductor.

5. A tubular conductor for a high frequency cable, comprising twosuperposed and mutually radially spaced co-axial layers, each of saidlayers comprising a strip of metal bent transversely to form anapproximately complete cylinder having transverse ribs projectingtowards and extending to the adjacent surface of the other of saidlayers and located between the ribs of said other layer, thelongitudinal edges of the strips lying parallel with the axis of saidtubular conductor..

6. A tubular conductor for a high frequency cable, comprising twosuperposed and mutually radially spaced V co-axial layer s, each of saidlayers comprising a strip of metal bent transversely to form anapproximately complete cylinder having transverse ribs projectingtowards and extending to the adjacent surface of the other of saidlayers and located between the ribs of said other layer, thelongitudinal edges of the strips running in a helix of long pitch.

7. A tubular conductor for a high frequency cable, comprising twosuperposed and mutually radially spaced co-axial component layers, eachof said layers comprising strip of metal bent transversely to form anapproximately complete cylinder having transverse ribs projectingtowards and extending to the adjacent surface of the other of saidlayers and located between the ribs of the said other layer, thetransverse ribs of at least one of said layers being skewed and the ribsof one of said layers being so positioned with respect to those of theother of said layers as to lock the two layers longitudinally.

8. A tubular conductor for a high frequency cable, comprising twosuperposed co-axial layers, each of said layers comprising a strip ofmetal bent transversely to form an approximately complete cylinderhaving plain cylindrical portions separated by transverse ribs eachprojecting towards and extending to the adjacent plain cylindricalportion of the surface of the other of said layers and located betweenthe ribs of said other layer, each rib on one of said layers forming apart of a helical screw thread and each rib on the other of said layersforming part of a screw thread of the same pitch as that of the firstsaid screw thread and over a part of its length in engagement with oneside of a rib on the first layer and over another part of its length inengagement with the other side of that rib.

9. A tubular conductor for a high frequency cable, comprising twosuperposed and mutually radially spaced co-axial layers, each of saidlayers comprising a strip of metal bent transversely to form anapproximately complete cylinder having plain cylindrical portionsseparated by transverse ribs each projecting towards and extending tothe adjacent plain cylindrical portion of the surface of the other ofsaid layers and located between the ribs thereof, the edges of the innerof said layers abutting against one another and the edges of the outerof said layers being separated by a small gap, and, means for tighteningdown the outer of said layers on to the inner of said layers and holdingthe edges of said inner layer in contact with one another, whereby theinternal diameter of said conductor is controlled by the width of saidstrip of which the inner of said layers is comprised.

10. A tubular conductor for a high frequency cable, comprising twosuperposed and mutually radially spaced co-axial layers, each of saidlayers comprising a strip .of metal bent transversely to form anapproximately complete cylinder having plain cylindrical portionsseparated by transverse ribs each projecting towards and extending tothe adjacent plain cylindrical portions of the surface of the other ofsaid layers and located between the ribs thereof, the edges of the innerof said layers abutting against one another and the edges of the outerof said layers being separated by a small gap, and a binder at least onetape extending helically around the outer of said layers and tighteningdown said outer layer on to the inner of said layers and holding theedges of said inner layer in contact with one another, whereby theinternal diameter of said conductor is controlled by the width of saidstrip of which the inner of said layers is comprised.

11. A tubular conductor for a high frequency cable, comprising twosuperposed and mutually radially spaced co-axial layers, each of saidlayers comprising a strip of metal bent transversely to form anapproximately complete cylinder having transverse ribs projectingtowards and extending to theadjacent surface of the other of said layersand located between the ribs of saidother layer, and means for holdingthe two layers in position comprising soldered joints between the ridgesof the ribs of at least one of said layers and the adjoining surface ofthe other of said layers.

12. A tubular conductor for a high frequency cable, comprising twosuperposed and mutually radially spaced co-axial layers, each of saidlayers comprising a strip of metal bent transversely to form anapproximately complete cylinder having transverse ribs projectingtowards and extending to the adjacent surface of the other of saidlayers and located between the ribs of said other layer, and means forholding the two layers in position comprising cemented joints betweenthe ridges of the ribs of at least one of said layers and the adjoiningsurface of the other of said layers.

13. A tubular conductor for a high frequency cable, comprising twosuperposed and mutually radially spaced co-axial layers, each of saidlayers comprising a strip of metal bent transversely to form anapproximately complete cylinder having transverse ribs projectingtowards and extending to the adjacent surface of the other of saidlayers and located between the ribs of said other layer, and meansuniting the ridges of the ribs of at least one of the layers to theadjoining .surface of the other of said layers, whereby to hold the twolayers in position relative to one another.

14. An electric cable for the transmission of high frequency electriccurrents, comprising a tubular conductor, at least one inner conductorwithin said tubular conductor and insulating means within said tubularconductor locating said inner conductor relative to said tubularconductor and insulating it therefrom, said tubular conductor comprisingtwo superposed and mutually radially spaced co-axial layers, eachcomprising a transversely bent strip of metal forming an approximatelycomplete cylinder, the inner of said layers having outwardly projectingtransverse ribs and the outer of said layers having inwardly projectingtransverse ribs, the ribs of both inner and outer of said layers beingapproximately equal in depth radially and fitting between each other,said layers and said ribs being so dimensioned that said layers arespaced apart by the depth of said ribs.

15. An electric cable for the transmission of high frequency electriccurrents, comprising a tubular conductor, at least one inner conductorwithin said tubular conductor and insulating means within said tubularconductor locating said inner conductor relative to said tubularconductor and insulating it therefrom, said tubular conductor comprisingtwo superposed co-axial component layers each of said layers comprisinga strip of metal bent transversely to form an approximately completecylinder having plain cylindrical portions separated by transverse ribseach projecting towards and extending to the adjacent plain cylindricalportion of the surface of the other of said layers and located betweenthe ribs of the said other layer, the transverse ribs of at least one ofsaid layers being skewed and the ribs of one of said layers being sopositioned with respect to those of the other of said layers as to lockthe two layers longitudinally.

16. An electric cable for the transmission of high frequency electriccurrents, comprising a tubular conductor, at least one inner conductorwithin said tubular conductor and insulating means within said tubularconductor locating said inner conductor relative to said tubularconductor and insulating it therefrom, said tubular conductor comprisingtwo superposed co-axial component layers each of said layers comprisinga strip of metal bent transversely to form an aproximately completecylinder having plain cylindrical portions separated by transverse ribseach projecting towards and extending to the adjacent plain cylindricalportion of the surface of the other of said layers and located betweenthe ribs of the said other layer, each rib on one of said layers forminga part of a helical screw thread and each rib on the other of saidlayers forming part of a screw thread of the sme hand and of the samepitch as that of the first said screw thread and over a part of itslength being in engagement with one side of a rib on the first layer andover another part of its length in engagement with the other side ofthat rib.

17. An electric cable for the transmission of high fre quency electriccurrents, comprising a tubular conductor, at least one inner conductorwithin the tubular conductor and insulating means within said tubularconductor locating said inner conductor relative to said tubularconductor and insulating it therefrom, said tubular conductor comprisingtwo superposed co-axial layers, each of said layers comprising a stripof metal bent transversely to form an approximately complete cylinderhaving transverse ribs projecting towards and extending to the adjacentsurface of the other of said layers and located between the ribsthereof, the edges of the inner of said layers abutting against oneanother and the edges of the outer of said layers being separated by asmall gap, and means for tightening down the outer of said layers on tothe inner of said layers whereby to ensure contact between the edges ofsaid inner layer and that the internal diameter of said conductor iscontrolled by the width of said strip of which the inner of said layersis comprised.

18. An electric cable for the transmission of high frequency electriccurrents, comprising a tubular conductor, at least one inner conductorwithin a tubular conductor and insulating means within said tubularconductor locating said inner conductor relative to said tubularconductor and insulating it therefrom, said tubular conductor comprisingtwo superposed co-axial layers, each of said layers comprising a stripof metal bent transversely to form an approximately complete cylinderhaving transverse ribs projecting towards and extending to the adjacentsurface of the other of said layers and located between the ribsthereof, the edges of the inner of said layers abutting against oneanother and the edges of the outer of said layer being separated by asmall gap, and a binder comprising at least one tape extending helicallyaround the outer of said layers and tightening down said outer layer onto the inner of said layers, whereby to ensure contact between the edgesof said inner layer and that the internal diameter of said conductor iscontrolled by the width of said strip of which the inner of said layersis comprised.

19. An electric cable for the transmission of high frequency currents,comprising a tubular conductor, an inner conductor within said tubularconductor and insulating means for supporting said inner conductor andmaintaining it in spaced relationship to said tubular conductor, saidtubular conductor comprising two superposed and mutually radially spacedco-axial layers, each of said layers comprising a strip of metal benttransversely to form an approximately complete cylinder havingtransverse ribs projecting towards and extending to the adjacent surfaceof the other of said layers and located between the ribs of said otherlayer and means for holding the two layers in position comprisingsoldered joints between the ridges of the ribs of at least one of saidlayers and the adjoining surface of the other of said layers.

20. An electric cable for the transmission of high frequency currents,comprising a tubular conductor, an inner conductor within said tubularconductor and insulating means for supporting said inner conductor andmaintaining it in spaced relationship to said tubular conductor, saidtubular conductor comprising two superposed and mutually radially spacedco-axial layers, each of said layers comprising a strip of metal benttransversely to form an approximately complete cylinder havingtransverse ribs projecting towards and extending to the adjacent surfaceof the other of said layers and located between the ribs of said otherlayer and means for holding the two layers in position comprisingcemented joints between the ridges of the ribs of at least one of saidlayers and the adjoining surface of the other of said layers.

21. An electric cable for the transmission of high frequency currents,comprising a tubular conductor, an inner conductor within said tubularconductor and insulating means for supporting said inner conductor andmaintaining it in spaced relationship to said tubular conductor, saidtubular conductor comprising two superposed and mutually radially spacedco-axial layers, each of said layers comprising a strip of metal benttransversely to form an approximately complete cylinder havingtransverse ribs projecting towards and extending to the adjacent surfaceof the other of said layers and located between the ribs of said otherlayer and means uniting the ridges of the ribs of at least one of thelayers of the Reieences Cited in the file of this patent UNITED STATESPATENTS 1,057,098 Smith Mar, 25, 1913 1,514,292 Knoderer Nov. 4, 19242,245,766 Dorfelet a1. June 17, 1941 2,469,565 Logan May 10,19492,546,309 Kempf Mar. 27, 1951 2,589,700 Johnstone Mar. 18,1952

. FOREIGN PATENTS 24,122 Great Britain of 1910

